ATmega32A Datasheet - Sunrom Technologies

ATmega32AThe CKSEL0 Fuse together with the SUT1:0 fuses select the start-up times as shown in Table 8-4.Table 8-4.CKSEL0Notes: 1. These options should only be used when not operating close to the maximum frequency of thedevice, and only if frequency stability at start-up is not important for the application. Theseoptions are not suitable for crystals.2. These options are intended for use with ceramic resonators and will ensure frequency stabilityat start-up. They can also be used with crystals when not operating close to the maximum frequencyof the device, and if frequency stability at start-up is not important for the application.8.5 Low-frequency Crystal OscillatorTo use a 32.768kHz watch crystal as the clock source for the device, the Low-frequency CrystalOscillator must be selected by setting the CKSEL fuses to “1001”. The crystal should be connectedas shown in Figure 8-2. By programming the CKOPT Fuse, the user can enable internalcapacitors on XTAL1 and XTAL2, thereby removing the need for external capacitors. The internalcapacitors have a nominal value of 36 pF.When this Oscillator is selected, start-up times are determined by the SUT fuses as shown inTable 8-5.Table 8-5.Start-up Times for the Crystal Oscillator Clock SelectionSUT1:0Start-up Time fromPower-down andPower-save0 00 258 CK (1) 4.1ms0 01 258 CK (1) 65ms0 10 1K CK (2) –0 11 1K CK (2) 4.1ms1 00 1K CK (2) 65ms1 01 16K CK –1 10 16K CK 4.1ms1 11 16K CK 65msSUT1:0Additional Delayfrom Reset(V CC = 5.0V) Recommended UsageCeramic resonator, fast risingpowerCeramic resonator, slowlyrising powerCeramic resonator, BODenabledCeramic resonator, fast risingpowerCeramic resonator, slowlyrising powerCrystal Oscillator, BODenabledCrystal Oscillator, fast risingpowerCrystal Oscillator, slowlyrising powerStart-up Times for the Low-frequency Crystal Oscillator Clock SelectionStart-up Time fromPower-down andPower-saveAdditional Delayfrom Reset(V CC = 5.0V) Recommended Usage00 1K CK (1) 4.1ms Fast rising power or BOD enabled01 1K CK (1) 65ms Slowly rising power10 32K CK 65ms Stable frequency at start-up11 Reserved8155C–AVR–02/1128